1. Field of the Invention
The present invention relates to a piston for an internal combustion engine for efficiently radiating heat from a head disposed inside of a combustion chamber.
2. Description of Background Art
A piston for an internal combustion engine is formed with a plurality of ribs on a reverse face (that is, a surface on the opposing side to the surface facing to the combustion chamber) of a head part for radiating heat generated when an air-fuel mixture is burned inside the combustion chamber to a crankcase side. Further, a piston must be provided for maintaining strength with respect to a combustion gas pressure.
As an example of the piston for an internal combustion engine, there is proposed Japanese Unexamined Utility Model Patent Publication S60-45643 xe2x80x9cPISTON FOR ENGINExe2x80x9d. The construction of this piston will be explained in detail with reference to FIG. 5 which illustrates a sectional view illustrating a piston for a conventional internal combustion engine. A piston 100 is provided with a cylindrical skirt part 102 to a lower part of a head part 101, formed with a pair of pin boss parts 103, 103 on both opposing side walls to each other of the skirt part 102, and a plurality of pieces of ribs 106 are provided on a surface 101a on a side opposing to a combustion chamber 105 of the head part 101.
A heat radiation property is enhanced by being provided with a plurality of pieces of the ribs 106 and by enlarging a surface area of the head part 101. In addition to that, by reinforcing the head part 101 with a plurality of pieces of the ribs 106, a wall thickness in the head part is thinned, and a weight reduction of the piston is realized. In this way, a fuel economy and the output of the internal combustion engine can be enhanced.
However, since the ribs 106 extend substantially at right angles downwardly from a head part, connecting parts of proximal end parts 106a of the ribs 106 with the head part 101 are formed with recesses substantially at an angle of 90 degrees. Therefore, stress is liable to be concentrated on the connecting part of the proximal end parts 106a of the ribs 106 with the head part 101.
Eventually, according to various types of an internal combustion engine, there is the possibility of cracks being generated in the connecting part of the proximal end parts 106a of the ribs 106 with the head part 101. Accordingly, in order to prevent the crack from being generated, for example, a piston 100 for an internal combustion engine is required to be formed from a quality of material that is high in a tensile stress, and that causes a factor to increase in cost.
Thus, an object of the present invention is to provide a piston for an internal combustion engine having a head part being enhanced in heat radiating property thereof while sufficiently maintaining the strength of the head part, and the weight reduction of the piston.
A piston for an internal combustion engine is constituted of a head part, a cylindrical skirt part ranged to a lower part of the head part, a pair of pin boss parts formed on both opposing side walls to each other of the skirt part, wherein, a plurality of pieces of the recessed parts, a cross section thereof being presented in a smooth circular arc, are formed in a surface on an opposing side to a surface facing to a combustion chamber of the head part described above.
A plurality of pieces of the recessed parts, the cross sections thereof being presented with smooth circular arcs, are formed on a reverse face of the head part. With this contrivance, a heat radiation property is enhanced by enlarging a surface area of the reverse face of the head part. In addition to that, the weight of the head part is lightened by forming a plurality of pieces of the recessed parts on the reverse face of the head part wherein a weight reduction of the piston for an internal combustion engine is realized.
Further, by forming the cross section of the recessed part with a smooth circular arc, when a combustion gas pressure is operated to the head part, stress is prevented from concentrating on the recessed part.
The outer peripheral part of the head part is a portion arranged to a skirt part, a wall thickness in the neighborhood of the outer peripheral part is thicker than the center of the head part. Accordingly, by forming the recessed parts in the neighborhood of the outer peripheral part of the head part, a wall thickness of the outer peripheral part is set close to a wall thickness of a central part.
By arranging the recessed parts in the shape of the lattice in the neighborhood of the outer peripheral part of the head part, a plurality of pieces of recessed parts are arranged efficiently in the neighborhood of the outer peripheral part. Thus, a wall thickness in the neighborhood of the outer peripheral part of the head part can be set close to a wall thickness in the center of the head part. Further, a surface area of the head part can be increased.
A width of a recessed part is denoted by the letter c, a height thereof is denoted by the letter h, a ratio between the width c and the height h, that is, h/c is set in a range of 0.15-0.25.
When the ratio h/c is smaller than 0.15, it becomes difficult to sufficiently enlarge a surface area of a head part and it is difficult to enhance heat radiation. Thus the ratio h/c is set equal to or more than 0.15, the heat radiation is tried to be enhanced by sufficiently enlarging the surface area of the head part.
Further, when the ratio h/c exceeds 0.25, it becomes difficult to form a cross section of the recessed part in a shape that is a smooth circular arc, stress can not be prevented from being concentrated. Thus, when the ratio h/c is set equal to or smaller than 0.25, by forming the cross section of the recessed part in a shape being presented in a smooth circular arc, stress is prevented from being concentrated.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.